The retinal photopigments of geckos will be further studied, examining their properties in situ as compared to these properties when solubilized. The effects of temperatures, mercurial reagents and anions, which have been investigated with the pigments in digitonin, will be examined with the pigments within the outer segments. The protective action of chloride against thermal destruction of the gecko 521-pigment when solubilized in Triton-X-100 will be further investigated. This action of chloride will be compared to the bathochromic effect of chloride with the view of deciding whether or not the same mechanism is involved in both chloride effects. In addition to geckos an attempt will be made to obtain more Arctic cod (Arctogadus borisovi) which has a rhodopsin remarkably sensitive to temperatures. The problem will be to determine whether or not chloride ions protect this rhodopsin against thermal degradation as they protect the gecko pigment when dissolved in Triton.